Glass half full?

On Jan. 1, I joined 15 friends on a raft trip down the Colorado River through the Grand Canyon. That morning, our boats were covered in snow; the canyon’s red cliffs, capped with white, looked like giant slabs of frosted carrot cake. The ranger said locals had never seen the place so wintry.

So we were delighted to return to Colorado — thousands of feet higher, where the river’s Rocky Mountain headwaters lie — and find no sign of winter. “Mountain biking in a tank top. Suck it, New England,” one of our trip leaders crowed from Durango on Facebook as a blizzard battered the East Coast.

But as the endless warm days slushed snow into mud and turned mud into hardpan, a growing alarm replaced our lizard-like impulse to bask. Between Jan. 25 and Feb. 8, 174 Colorado communities met or broke high temperature records. A few on the state’s eastern plains even neared or surpassed 80 degrees Fahrenheit.

The Colorado River, which supplies 40 million people and a $1.4 trillion economy, is already gripped by one of the worst droughts in 1,200 years, so the balmy weather doesn’t bode well. And Lake Mead, the giant reservoir that supplies Las Vegas, may this year drop dangerously close to an official shortage.

This was among the grim possibilities that Patricia Mulroy, the former head of the Southern Nevada Water Authority, spent the latter half of her 25-year career preparing for. Now, a year after her retirement, cover story writer Matt Jenkins looks back at Mulroy’s long fight to ensure that Vegas retained enough water to feed its growth even as the Colorado River shrank. Though many readers associate Vegas with selfish excess, Mulroy used its predicament to help push the river’s water managers into a new era of deal-making and shared sacrifice. The goal is to stretch existing supplies as far as possible — with the side benefit of lessening the need for expensive and environmentally damaging new water infrastructure.

Though Mulroy has moved on, that part of her legacy is increasingly relevant: A NASA study released Feb. 12 suggests that if greenhouse gas emissions continue to rise at current rates, the Southwest and Central Plains have an 80 percent chance of succumbing to multi-decade megadrought in the latter half of this century. “There are degrees of screwed,” Peter Gleick of the Pacific Institute pointedly told Slate, “and this paper suggests we’re falling off the cliff.”

Maybe. But how far we fall, and the severity of impact, may depend on how we choose to adapt — especially as Congress continues to ignore climate change. Mulroy reminds us that looming disaster can be a catalyst for change: A glass half-empty is still a glass half-full. So how will we make the best of this dry new normal — one where any snow along the Colorado, even in the Grand Canyon, must be seen as an ever more precious blessing?